This invention relates to a coating device and process, and in particular, to an improved system comprising a trough and a cylindrical applicator for applying fluid to a moving web.
Devices for applying fluids to a moving web are well known. For example, roll coating is one of the common techniques for continuously applying a liquid film onto a moving sheet. Roll coating apparatus often utilize gravure applicators to apply a very thin coating to a moving web. These gravure applicators are generally cylindrical and have an etched surface. These etched surfaces comprise valleys or cells which are filled with an unmetered quantity of the coating material applied from an adjacent roller or by rotating the gravure applicator in a bath of the coating material. A doctoring or wiper blade may be employed to regulate the amount of solution in the cells on the surface of the gravure applicator. As the cylinder rotates, the wiper or doctor blade removes all the excess coating from the surface leaving a measured amount of liquid in the recessed areas or cells. Approximately half of this measured amount of liquid in the recessed are as or cells is then transferred from the cells to a moving web by means of hydro-dynamic forces of a fluid having appropriate rheological characteristics such as fluid/solid and fluid/air surface tensions. These rheological characteristics are synchronized with variables such as applicator roll diameter, web surface speed and viscosity of the coating fluid being applied.